1. Field of the Invention
The present invention relates to an image forming apparatus, such as an electrophotographic apparatus and an electrostatic recording apparatus. The invention also relates to a developer detection apparatus to detect the presence and absence or the remaining developer used for such image forming apparatus.
2. Related Background Art
Conventionally, the image forming apparatuses used for an electrophotographic apparatus have been often provided with a developer detection apparatus for detecting the amount of the remaining developer including the presence and absence of the developer.
As the method for detecting the amount of the remaining developer adopted for a developer detection apparatus of the kind, there are an optical method using the light emitting device and photodetecting device together; an electrostatic capacitance method whereby to detect the electrostatic capacitance of the developer; a piezoelectric method whereby to detect the pressure exerted by the developer by means of vibration; and some other various methods which have been proposed and put into practice.
Also, conventionally, there has been put in practice a cartridge method whereby to form at least an image bearing body and a developing device integrally to make them detachably mountable on the main body of an image forming apparatus. In this case, when the developer is completely consumed, the cartridges are replaced.
In this cartridge method, it is preferable to install or provide a detection sensor on the main body of the apparatus for the detection of the amount the remaining developer in the cartridge so that the detection sensor can be used repeatedly. In order to implement this method, it is generally and widely practiced to adopt a magnetic permeability sensor (toner sensor) as a detection means for detecting the magnetic permeability of the developer contained in a developer container from its outer side by the utilization of the magnetism of the developer in order to detect it by means of the voltage changes thereof.
The toner detection means for detecting the amount of the remaining developer using such toner sensor is shown in FIG. 14 as disclosed in Japanese Patent Application Laid-Open No. 3-264974. This means is aimed at repeatedly using the expensive toner sensor separately from the developing device which is made replaceable as an expendable component. Then, this means comprises a shaft 106 that rotates clockwise or counterclockwise while being interlocked with the opening or closing of the upper structure 107 which forms the cover of the developing device; an elastic member 105 fixed to one end of this shaft 106; and the toner sensor 120 fixed to the swingable holder 101 to detect the amount of the remaining toner. Then, interlocked with the closing of the upper structure 107, the shaft 106 rotates to swing the holder 101 by the biasing force exerted by the elastic member 105. The toner sensor 120 is allowed to be in contact with the toner detection point of the developing device in order to detect the amount of the remaining toner. Also, interlocked with the opening operation of the upper structure 107, the shaft 106 rotates to release the biasing force exerted by the elastic member 105. Thus, the holder 101 and the toner sensor 120 are allowed to part form the toner detecting point.
When the magnetic permeability sensor (toner sensor) is used to detect the magnetic permeability of the developer from the outer side of the developer container with the changes of voltage by the utilization of the magnetism of the developer, the close contact between the developer container and the detection surface of the sensor is extremely important. Particularly, the extremely fine changes in the gap between the magnetic permeability sensor and the developer container may result in a greater output fluctuation. There is a need for obtaining a closer contactness between them.
In this respect, if there are errors in the installation of the sensor, the looseness along with the attaching and detaching of the developer container, the variation of biasing force exerted on the sensor with respect to the developer container, or the like, the contact between the sensor and the developer container tends to be lower. Then, the resultant accuracy of detection is lowered eventually.
In the method, such as disclosed in Japanese Patent Application Laid-open No. 3-264974, in which interlocked with the closing operation of the upper structure, the shaft rotates to swing the holder by biasing force exerted by the elastic member, and the toner sensor is placed to be in contact with the toner detection point in the developer container, there are some cases where the appropriate positional relationship is not obtainable between the developer container, the sensor, and the elastic member due to the accumulated variations of the dimensional precision and errors in installation of each of the plural members, such as the upper structure, shaft, holder, and elastic member.
In such a case, the amount of deformation of the elastic member varies greatly when the cover is closed. Along with such variation, the basing force of the sensor is caused to vary greatly, hence making it difficult to obtain the appropriate contacting force that should be exerted by the sensor.
If the contacting force of the sensor is weak, it becomes impossible to obtain close contact between the developer container and the detection surface of the sensor. On the contrary, if the contacting force becomes too strong, the developer container, the holder, and the toner sensor itself tend to be distorted. As a result, the close contact can hardly be obtained, hence making it impossible to secure the exact sensor output.
Also, there is a drawback that may hinder obtaining close contact between the contact surface of the developer container and the detection surface of the sensor themselves if the angular deviation takes place between them, because the detection surface of the sensor may be biased in abutting upon the developer container.